Concessions do not apply in strokeplay – you (and your fellow competitors) must hole out at each hole to return a score for that hole.
In matchplay, a player may concede their opponent’s next stroke, a hole, or the match at any time. Concessions must be clearly communicated and are final – they cannot be declined or withdrawn, so there is no issue if, for example, you miss a putt that has been conceded. You can also agree to halve a hole, but only after at least one player has started play of that hole.
There are a couple of things you specifically aren’t allowed to do:
- agree to concede holes to each other to deliberately shorten a match
- agree that all putts within a certain length (e.g. a putter grip) will be conceded (you may only concede the next stroke)
In strokeplay, if you are uncertain how to proceed under the rules you can play more than one ball (having declared which one you wish to count before playing any strokes after the uncertainty arose) and seek a committee decision after the round. You do not have this option in matchplay.
In matchplay you must decide how you want to proceed. If you follow your opponent’s advice then the result of the hole will stand. If you choose to follow your own decision you will need to seek a decision from the committee after the round. If you have proceed correctly under the rules then the result of the hole will stand. However, if you followed a procedure that was not allowable under the rules you will have lost the hole. This can lead to the strange situation of not knowing whether you are 1 up or 1 down playing the last hole!
In summary, when playing a match it is your responsibility to protect your own interests under the rules – if you do not know the rules (and the local rules), or have access to some help (I recommend the R&A Rules App) then you simply can’t do it!